The present invention relates to the manufacture of metal parts, such as headers and steam drums, to which tubes are to be attached. More particularly, it relates to a method of providing nipples for the attachment of tubes to relatively thick parts.
In the manufacture of steam drums and headers, tubes must be attached around holes in the header or drum. Since welding of a tube directly to a drum or header results in the requirement that a time-consuming heat treatment be provided, it is preferable in many cases to attach the tubes to nipples formed around the hole in the part to which the tube is to be attached. One method of providing the nipple is to drill a hole through the part and then force a mandrel of slightly greater diameter than the initial hole through the hole, the material forced through the hole by the mandrel thereby forming a nipple on the surface of the part. While this approach is quite practical for thin parts, the probability that the part will tear increases with increasing part thickness. Accordingly, an improved method is needed for dealing with relatively thick parts.